A redundant array of independent disks (RAID) technology is a data storage scheme that divides and replicates data among multiple hard disk drives. The RAID technology increases data reliability and input/output (I/O) performance by using techniques such as mirroring, the copying of data to more than one disk; striping, the splitting of data across more than one disk; and error correction, where redundant data is stored to allow errors to be detected and possibly fixed. Different RAID levels use one or more of the techniques, depending on their respective system requirements.
Although redundancy based on the mirroring, striping and/or error correction may improve the data reliability, it allows less data to be stored. For instance, a two disk RAID level 1 array may lose half of the total capacity that would have otherwise been available using both disks independently, and a RAID level 5 array with several disks may lose the capacity of one disk for the error correction.